It is well known that the voltage supplied by a vehicle battery to on-board control and data processing systems fluctuates according to temperature, load, battery age, proximity to overhead power lines, and other environmental factors, and that this tends to distort the measurements relied upon by the system in generating proper control signals. The input/output (I/0) circuits of such systems, especially in motor vehicles, typically use analog-operating comparators for recognition and preparation of input signals to the control circuits. These comparators monitor the relationships between various kinds of analog input signals and respective threshold values for each.
Depending upon a computer program and the operating states of the engine to be controlled, the input/output circuits generate variable duty cycles or keying ratios with programmable repetition rates, for example to match the output control signal rate to a changed engine RPM. In vehicular control systems, it is particularly important to generate a number of output signals at exactly specified times to, for example, optimally control fuel injection.
In conventional input/output circuits, a large number of discrete electronic components must be interconnected in order to carry out the multitude of signal processing and control tasks required.